JP2002535132A - Microporous hollow fiber membranes formed from fluorinated thermoplastic polymers - Google Patents

Abstract

  (57) [Summary] A highly fluid porous hollow fiber membrane is obtained by heating the polymer from a fluorinated thermoplastic polymer, directly extruding a solution having a lower critical solution temperature into a cooling bath, and performing liquid-liquid phase separation. Manufacture through. Extrusion can be performed vertically or horizontally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a process for producing a microporous hollow fiber membrane from a fluorinated thermoplastic polymer. In particular, it relates to a process for producing a microporous membrane essentially free of a coating on at least one of an inner surface and an outer surface, and a produced fiber membrane.

[0002]

[Prior art]

Microporous membranes are used in a wide range of fields. When used as a separation filter, it can be used to remove particles and particles from ultrapure water and organic solvents in dispersions such as buffers, solutions containing therapeutic agents in the field of pharmacy, microelectronics, wafer manufacturing processes, and water purification processes. Bacteria and the like can be removed.
In addition, when the microporous membrane exhibits high adsorption and wicking characteristics with high porosity, it can be used in the field of medical devices.

Further, the hollow fiber membrane can be used as a film contactor, particularly a film contactor used for a degassing or gas adsorption device. The contactor produces two phases. That is,
It is composed of two liquid phases, or a liquid phase and a gas phase, and is configured to transport a composition component from one phase to the other phase. A common step is a mass transport step between the gas phase and the liquid phase, in which components in the gas phase, that is, the gas stream are adsorbed in the liquid phase. In the liquid phase degassing step, a liquid phase containing a dissolved gas component comes into contact with the atmosphere, a vacuum atmosphere, or a separated phase to remove the dissolved gas component.

[0004] Examples of conventional gas adsorption include generating gas bubbles in an adsorbed liquid phase, increasing an interface area between a gas phase and a liquid phase, and increasing a transport speed of a substance to be adsorbed from a gas phase. Can be. Conversely, droplets can be sprayed, and the liquid phase can be transported through a thin film in a countercurrent operation such as a spray tower or a pack tower. Similarly, immiscible droplets can be dispersed in the second liquid phase, improving transport efficiency. Packing columns and tray columns have the disadvantage that the individual transport speeds in the two phases cannot be independently controlled without performing operations such as loading and entrainment. However, if the two phases can be separated using a coating, the transport speed of each phase can be varied independently. Furthermore, the entire area can be used, even at relatively low transport speeds. In view of these advantages, the demand for hollow fiber membranes for contactors is increasing.

[0005] Hydrophobic microporous membranes can be used for contactors with aqueous solutions. In this case, the microporous membrane does not show wettability to the aqueous solution. The aqueous solution is
The mixed gas having a lower pressure than the aqueous solution flows on one side of the microporous membrane and flows on the other side of the microporous membrane. The pressure on each side of the microporous membrane is maintained such that the pressure of the liquid does not exceed the critical pressure of the membrane and the gas does not bubble in the liquid. The critical pressure, which is the pressure at which the aqueous solution enters the pores, depends directly on the material constituting the coating, is inversely proportional to the pore diameter of the coating, and is proportional to the surface tension of the liquid phase in contact with the gas phase.

[0006] Hollow fiber membranes are mainly used for this purpose because they can seal the devices described above at high density. The encapsulation density depends on the percentage of the surface area that exhibits a filtering action per unit volume of the device. Also, the hollow fiber membrane may function as a feeder in contact with the inner or outer surface of the device. In this case, a more advantageous effect may be exhibited. When brought into contact with the coating system, dissolved gas components can be removed from the liquid phase, that is, degassing operation can be performed, and gas substances can be added to the liquid phase. For example, ozone can be added to ultrapure water for cleaning a semiconductor wafer.

[0007] Microporous membranes exhibit higher mass transportability than non-porous membranes and can be preferably used for many applications. When used for a liquid having a low surface tension, a material having a relatively small hole diameter is used because penetration resistance increases. When used for transporting gases that are highly soluble in the liquid phase, the mass transport resistance of the coating is an obstacle to effective mass transport.

[0008] Z. Qi and ELCussler have announced that film resistance can control the adsorption of gaseous components such as ammonia, SO ₂ and H ₂ S in sodium hydroxide solution (
J. Membrane Sci. 23 (1985) 333-345). This seems to work in contactors where the adsorption liquid is a strong acid or base. In contactor applications, porous contact membranes such as microporous membranes are preferably used because they have a somewhat reduced film resistance. In the case where the liquid has a high resistance so that the liquid does not enter the pores, it is within a very practical range. The very low surface tension materials used in the present invention can be used without manipulation if the fiber surface is covered with a low surface tension material, which is an additional and complicated manufacturing process.

The advantage of using the microporous membrane or the like for such a contactor is that the extremely low surface tension property of the fluorinated polymer can be used together with a low surface tension liquid. For example, highly corrosion resistant developers used in the field of the semiconductor manufacturing industry may contain surface tension reducing additives such as surfactants. Since such a developer may penetrate and penetrate into the pores under the working pressure, the solution may partially be lost and may be excessively evaporated. Cannot do it.

[0010] In addition, the pores into which the liquid has entered increase the mass transport resistance with respect to the transport of gaseous components. In USP 5,749,941, conventional hollow fiber membranes, such as polypropylene and polyethylene, use a solution additive to prevent leakage when adsorbing carbon dioxide or hydrogen sulfide in an aqueous solution containing an organic solvent. It is described that it cannot be used unless it is used. While PTFE membranes are effective for such applications, they are difficult to process into hollow fibers, presumably due to their low surface tension. The membrane of the present invention has the same surface tension as PTFE and can easily produce a hollow membrane having a small pore size.

The microporous membrane has a continuous porous structure that penetrates the inside of the membrane. Workers in this field have a range of pore sizes from 0.05 μm to 10.0 μm. Such a membrane can be formed into a sheet shape, a tubular shape, or a hollow fiber shape. Hollow fiber is
It has the advantage that it can be incorporated into a densely sealed separation device. The sealing density depends on the ratio of the surface area acting as a filter to the volume of the device. Further, the hollow fiber may function as a feeder in contact with an inner surface or an outer surface of the device. In this case, a more advantageous effect is exhibited.

The hollow fiber porous membrane has an outer diameter and an inner diameter corresponding to the thickness of the wall surface forming the pore. The inner diameter defines the hollow portion of the hollow fiber and is used to introduce a fluid component. Then, it is fed through the wall surface of the hole, and when filtering is performed from the outer surface, it permeates through the wall surface. The interior hollow portion may be referred to as the "lumen."

The outer surface of the hollow fiber membrane has a skin component, and the inner surface has no skin component. Epidermis refers to a thin dense surface layer associated with the membrane substructure. In membranes having an epidermal component, most of the resistance to flow through the membrane is in the epidermal portion. The skin portion of the microporous membrane has pores that form the continuous porous structure of the substructure. In the microporous membrane having a skin component, the portion occupied by the pores is a small portion of the surface. The membrane having no skin component is porous, and pores are formed on most of the surface. The porosity is composed of single pores or void regions formed by connecting single pores. The porosity here means the surface porosity, and is defined by the surface area ratio of the whole pores opened on the surface of the membrane.

[0014] Microporous membranes are classified as symmetric or asymmetric, depending on the uniformity of the pores passing through the membrane. In the case of a hollow fiber membrane, it has a porous wall surface composed of the fibers. Symmetric fiber membranes have a uniform pore size essentially over the entire cross section of the membrane. In the case of an asymmetric fiber membrane, the pore size exhibits a structure distributed over the entire cross section of the membrane. Asymmetry can also be defined from the ratio of the pore size on one surface to the pore size on the other surface.

[0015] Manufacturers produce microporous membranes from a variety of materials, most commonly using synthesized polymers. The most important of these polymers is the thermoplastic polymer.
The polymer exhibits fluidity when heated and can be molded. And
Upon cooling, its original solid state properties can be restored. When the conditions for using the microporous membrane become severe, usable materials are also limited. For example, in the microelectronics industry, organic solvent-based solutions used for wafer coating dissolve or swell and weaken most polymer films.

[0016] Hot stripping baths in the same field are composed of strong acids and oxidizing compounds. This destroys the polymer film. Polytetrafluoroethylene-fluoroalkyl vinyl ether copolymer (POLY (PTFE-CO-PFVAE)) or polytetrafluoroethylene-hexafluoropropylene) (FEP) is not adversely affected even under severe use conditions As such, it has advantages over membranes made from polymers that are less chemically and thermally stable.

Because of their chemical inertness, POLY (PTFE-CO-PFVAE) and FEP polymers are difficult to form into films using typical solution casting methods. These polymers can be made by using a thermally induced phase separation (TIPS) process. As an example of a TIPS process, a polymer and an organic solvent are mixed in an extruder and heated to a temperature at which the polymer decomposes. The membrane is formed by extruding through an extrusion mold. The extruded film cools and gels. During the cooling of the polymer solution, the temperature is reduced to below the upper critical solution temperature. At or below this temperature, two phases are formed from the uniform heated solution. One phase is the first polymer phase and the other phase is the first solvent phase.
Under appropriate conditions, the solvent-rich phase forms a continuous, penetrating, porous structure. This solvent-rich phase is extracted and the selected membrane is dried.

[0018] POLY (PTFE-CO-PFVAE) and FEP membranes produced by the TIPS process are described in USP 4,902,456.
Nos. 4,906,377, 4,990,294, and 5,032,274. USP4,902
No. 4,456, and US Pat. No. 4,906,377 describe that the membrane has a crack-like opening or a high-density surface phase with single or connected pores. USP 4,990,294 and US
P5,032,274 discloses that a separation solvent is coated when a formed membrane is present in a mold. In both cases, the membrane surface is composed of a dense surface layer with porous regions. In one example, a membrane made without co-extrusion in sheet formation stretches laterally. The surface of the film exhibits a nodular structure separated by crack-like openings.

US Pat. No. 5,395,570 discloses making hollow fiber membranes by extrusion. Specifically, using a quadrupole extrusion head, the hollow fibers are extruded together with a lumen filling solution, a coating layer, a cooling solvent, and the like. This method requires a complicated extrusion head and complicated control means. Further, it is necessary to form a separation coating layer composed of the solvent component between the cooling solvent and the extruded fiber membrane. Further, the extruded fiber membrane is not immediately contacted with the cooling solvent, but rather after passing through the lower portion of the extrusion head.

US Pat. No. 4,564,488 discloses a process for preparing a porous fiber and a porous membrane. This step involves forming a homogeneous mixture of the polymer and a solution inert to the polymer. The mixture must have a temperature region that exhibits complete miscibility, and must have a temperature region that causes a miscibility gap. The mixture is extruded at a temperature above the separation temperature, preferably into a bath containing the whole or mostly inert liquid. The inside of the bath is kept at or below the separation temperature. However, it is neither disclosed nor claimed that the homogeneous mixture is immediately or entirely extruded into a bath filled with an inert solution. The general-purpose polymer within the disclosure range of the patent does not describe the fluorinated thermoplastic polymer. Nor does it mention a method that requires immediate extrusion from a hot state to a cooling bath.

WO 95/02447 discloses an asymmetric PTFE membrane. The PTFE membrane is coated on a predetermined substrate with a PTFE solution in cycloalkane fluoride heated to about 340 ° C., and the solvent is applied such that one side of the membrane is less porous than the other. While removing, the PTFE is cooled. Then, the substrate is removed. There is no mention of using this method for unsupported hollow membranes.

US Pat. No. 4,443,116 discloses a process for making a porous fluorinated polymer structure. Polymers that can be used include sulfonyl fluoride groups (—SO ₂ F), sulfonates (SO ₃ Z), or copolymers of tetrafluoroethylene and vinyl fluoride ethers having a carboxyl functional group (COOZ). Here, Z represents a cation.
Polar functional groups promote solubility. Heat-induced phase separation is used when the solvent must be crystallized after cooling and phase separation. The solvent is removed in a solid state. No data is provided on the porous structure or permeability.

PTFE, POLY (PTFE-CO-PFVAE), and FEP sheet membranes are disclosed in US Pat. No. 5,158,680. There, an aqueous solution in which 1 μm or less of particulate PTFE is dispersed and a filamentous polymer are mixed to form a film, and after being heated to a melting temperature or higher, the filamentous polymer is heated. Is described.

In the filtration of ultrapure water, it is necessary that extremely low levels of extraction residues are removed from the membrane. The TIPS process requires only removal of the low molecular weight extrusion solvent after extrusion. This substance can be easily removed by extraction with a solvent. Since POLY (PTFE-CO-PFVAE) and FEP are inactive against the extraction solvent, no change in membrane characteristics occurs. Due to the porosity of the membrane and the high diffusivity of the low molecular weight solvent, extraction can be performed easily and completely. A membrane produced by extraction from a polymer or resin meets the inherently difficult requirement of removing a polymer or resin with a low diffusion rate.

The conventional POLY (PTFE-CO-PFVAE) film and the FEP film manufactured through the TIPS method have been required to be extruded from an air gap. POLY made by TIPS process
(PTFE-CO-PFVAE) membrane and FEP membrane are USP 4,902,456, USP 4,906,377, USP 4,990,294,
And USP 5,032,274. U.S. Pat. Nos. 4,902,456 and 4,906,377 describe that the membrane has a crack-like opening or a high-density surface phase with single or connected holes. US Pat. No. 4,990,294 and US Pat. No. 5,032,274 disclose that a separated solvent is coated when a formed membrane is present in a mold. In one example, the sheet-like film expands and contracts in the lateral direction. Rapid evaporation of the solvent at high extrusion temperatures produces a skin on the membrane,
It becomes impossible to sufficiently control the surface porosity.

To overcome this skin problem, a solvent coating method and a post-stretching method have been adopted by the inventor. In the solvent coating method, a solvent, a hot halogenated carbon oil heated to about 300 ° C., is used to coat the surface of the melt as soon as it dissolves in the mold. On the other hand, this method suppresses evaporation and causes other process problems. First, it is very difficult to coat a molten surface uniformly with a hot solvent because hot halogenated carbon oils tend to form droplets. Instead of providing a uniform coating, the thermal solvent coating may be streaked to the molten surface. After the solution has cooled and solidified, the surface of the membrane has an uneven, porous shape due to uneven application of the solvent. Second, the temperature of the oil is not uniform, and the properties of the obtained film are greatly changed due to non-planar cooling and hardening of the surface. Third, the hot oil is
The extruded melt tends to soften and the extruded fibers tend to break apart during processing.

It has been disclosed in US Pat. Nos. 4,990,294 and 5,032,274 that a technique called post-stretching treatment can improve the permeability of a PFA membrane having an epidermis. While stretching can substantially increase permeability, it has undesirable side effects. First, in order for stretching to be effective,
It is necessary that the film having the underlying skin portion is uniform in thickness and strength. As the film is stretched, the non-uniformity of the underlying film is further increased. The reason for this is that under the same stretch strength, the weaker part is stretched more than the strong part. As described above, it is difficult to form a film using a solvent coating technique. Without solvent coating technology, a large amount of porogen can be deposited to produce a dried polymer on a die lip. The deposited dry polymer scratches the melt surface, creating linear potential weaknesses in the film. In stretching, such a film sometimes separates and breaks from the linear weak portion.

Therefore, it is desirable to rapidly evaporate and remove the solvent from the fiber surface, and it is difficult to use a coating technique or a stretching technique. In order to increase the permeability and the holding power, it is preferable to use the entire surface of the membrane as efficiently as possible. To this end, it is preferable to produce a membrane having a high surface porosity without a skin portion.

Furthermore, in order to achieve the purpose of transporting a highly soluble gas component into a liquid phase having a low surface tension, it is preferable to use a porous hollow fiber contactor.

[0030]

Means for Solving the Invention

The present invention has a high fluidity and a skin-free hollow fiber membrane having no skin, and furthermore, a microporous membrane is made of a fluorinated thermoplastic polymer, particularly, a polytetrafluoroethylene-fluorinated alkyl vinyl ether copolymer. Manufactured from (POLY (PTFE-CO-PFVAE)) or polytetrafluoroethylene-hexafluoropropylene (FEP),
provide. These films can be used in harsh chemical environments without any problems. When compared to prior art membranes, the membranes of the present invention exhibit a high surface porosity and a high permeability or flow.

As one embodiment of the present invention, a fluorinated thermoplastic polymer, in particular, a polytetrafluoroethylene-fluoroalkylvinylether copolymer (POLY (PTFE-CO-PFVAE)) or polytetrafluoroethylene-hexafluoro Manufacture and provide porous hollow contactor membranes from (propylene) (FEP) and further provide their use.

Further, a method for producing these films is provided. This production method uses a thermally induced phase separation in producing a porous structure and a porous membrane.
: TIPS) method. A mixture of polymer pellets, ground to a smaller size than supplied by the manufacturers, and a solvent, such as a chlorotrifluoroethylene oligomer, is mixed until a paste or paste is formed. The polymer is
It is mixed to be approximately 12% to 35% by weight. The solvent is selected such that when the resulting solution is extruded and cooled, film formation occurs in a liquid-liquid phase rather than a solid-liquid phase.

Preferred solvents are saturated low molecular weight polymers of chlorotrifluoroethylene.
Specifically, Halocarbon Products Corporation, River edge, NJ brand name HaloV
ac60. In the heating step for forming the upper critical solution temperature, a solvent capable of dissolving the polymer is selected. However, it is required not to boil excessively at that temperature.

[0034] Fiber extrusion is referenced by spinning, and the extruded fiber length from the mold exit to the take-off is referenced by a spin line. The paste is filled into a heated extruder barrel that is weighed in a predetermined amount. Since the inside of the barrel is heated above the upper critical solution temperature, the paste is decomposed. The homogeneous solution is then extruded directly through an annular mold into a liquid cooling bath. The liquid cooling bath is maintained at a temperature equal to or lower than the upper critical solution temperature of the polymer solution. Preferred liquid cooling baths do not show solubility in the thermoplastic resin even at the extrusion temperature.

In the cooling process, the solution formed by heating undergoes phase separation, and gel-like fibers are formed. The mold tip is slightly sunk with respect to vertical spinning. That is, the spin line is lowered. For horizontal spinning, specially designed dies are used. In horizontal spinning, the spin line is maintained in the horizontal direction and is held at least in the plane up to the first guide roll. The mold is firmly fixed to the insulated wall and the mold tip passes through an opening with a liquid seal in said insulating wall. A trough for cooling the liquid flow is arranged in the recess on the side facing the insulating wall so that the mold nose outlet maintains the above-mentioned sunk state. The coolant flows through the trough and overflows into a relatively shallow region of the trough. Then, the mold nose outlet is kept in a state of being immersed in the cooling medium. In both the vertical spinning and the horizontal spinning described above, a booster heater and a temperature control means are used so as to prevent excessive cooling and to easily raise the solution temperature. The decomposed solution is then removed by extraction,
The resulting hollow fiber membrane is dried under conditions that do not cause membrane shrinkage or breakage. The drying temperature is 200-300C.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION

Those skilled in the art of manufacturing porous membranes, according to the teachings of the present invention,
It will be appreciated that hollow porous membranes without skin portions can be made from fluorinated thermoplastic polymers. In the present invention, the fluorinated thermoplastic resin is dissolved in a solvent to produce a solution having an upper critical solution temperature. Then, when the solution is cooled, it is separated into two phases by liquid-liquid phase separation. Examples of such a polymer include a polytetrafluoroethylene-fluorinated alkyl vinyl ether copolymer (POLY (PTFE-CO-PFVAE)) or polytetrafluoroethylene-hexafluoropropylene (FEP). PFA Teflon (registered trademark) is a specific example of the polytetrafluoroethylene-fluorinated alkyl vinyl ether copolymer, and in this case, the alkyl group is mostly or entirely a propyl group. FEP Teflon (registered trademark) is a specific example of polytetrafluoroethylene-hexafluoropropylene. Both are provided by DuPont.

[0037] Neofron PFA (Daikin Industries) is a polymer similar to PFA Teflon (registered trademark). When the alkyl group of the polytetrafluoroethylene-fluorinated alkyl vinyl ether copolymer is mainly a methyl group, USP5,4
63,006. A preferred polymer is the PTFE / PFVAE copolymer Hyfr.
on620 and provided at Ausimont USA, Inc., Thorofare, NJ.

For PTFE / PFVAE copolymer, PFA and FEP, a saturated low molecular weight polymer of chlorotrifluoroethylene has been found to be the preferred solvent. Specifically, Haloca
HaroVac60 trade name provided by rbon Products Corporation, River Edge, NJ.

The spinning component polymer and the solvent are mixed so that the solvent has a preferable weight ratio with respect to the polymer to form a paste, and the paste is filled in a container. The polymer is pulverized into particles having a size of 100 to 1000 μm, preferably 300 μm, by an appropriate pulverization process. If the particle diameter is too large, the particles cannot be completely dissolved in a preferable heating step, and long-time heating is required. If the particle size is too small, a high-cost pulverization process is required, and the entire manufacturing process becomes expensive. The polymer comprises about 12-35% by weight in the mixture. 35% by weight
When it exceeds, the optimal porosity cannot be obtained, and when it is less than 12% by weight,
The strength of the obtained fiber membrane deteriorates.

As a saturated low molecular weight polymer of chlorotrifluoroethylene, a trade name of HaroVa
c60 (Halocarbon Products Corporation). As the solvent, a solvent capable of dissolving the polymer when heated to the upper critical solution temperature is selected. However, it is required not to boil excessively at that temperature. When the polymer is dissolved at a temperature equal to or higher than the boiling point of the solvent, bubbles are generated during extrusion, and the spin line is broken. The solvent did not need to be composed of a purely single component, but rather mixed low molecular weight polymers of chlorotrifluoroethylene with different molecular weights or mixed with different copolymerization ratios. Those can also be used. Such a mixture is adjusted so that solubility and boiling point characteristics are in harmony.

Melting and Extrusion The paste is filled in a predetermined amount in a heating and mixing area of a general-purpose double screw extruder, and is heated under an inert atmosphere, preferably under a nitrogen atmosphere, in order to prevent deterioration of the solvent.
Heat to a preferred temperature between about 270-320C, more preferably to 285-310C. The heating temperature depends on the melting temperature of the polymer used. The extruder conveys the heated solution to an in-line heating metering pump and supplies the solution to an annular mold to control the extrusion speed. As appropriate, an in-line filter can be used.

When fabricating a fiber extruded hollow fiber membrane, a difficult situation not encountered in the process of fabricating a sheet-like membrane is encountered. When producing a sheet-like film, it is supported in a predetermined state until the target film is solidified. When fabricating a hollow fiber membrane at a high temperature, the above-mentioned problems become more serious. The hollow fiber membrane is formed by extruding a polymer solution or a polymer dispersion from a groove portion of a mold composed of concentric double tubes. The inner tube carries a liquid or gaseous component and maintains an inner diameter that defines a lumen during the solidification process.

In actual operation, the polymer solution is co-extruded with a rumen solution into a liquid bath. In the thermally induced phase separation method of the present invention, the liquid bath is maintained at a temperature such that the polymer solution to be used undergoes phase separation. After the formed solution is cooled and phase separation is performed, the obtained fiber is solidified. Unlike a flat sheet-like membrane coated or extruded on a roll or web-like carrier, or a tubular membrane formed on the inner or outer surface of a mandrel, an extruded hollow fiber membrane is not solidified during solidification. Not supported. The extruded solution is not supported, so
The driving force for transporting the fibers through the cooling bath acts directly on the formed solution as it solidifies. If the driving force is too large, the fibers will be separated.

There are two interconnected problems that need to be overcome in the fiber membrane manufacturing method of the present invention. These are indispensable in producing a highly permeable surfaceless film and in extruding a solution having sufficient strength to be continuously produced at a practical speed. Fluorinated thermoplastics melt at high temperatures of about 260-300 ° C., but are difficult to dissolve. Very few solvents are known to be soluble, and even saturated low molecular weight polymers of chlorotrifluoroethylene have certain limitations. As the molecular weight increases, the boiling point also increases. It is commonly recognized that in the TIPS process, the boiling point of the solvent is 25-100 ° C. above the melting temperature of the polymer and that it does not volatilize significantly at the extrusion temperature (Lloyd, DR et al, J. Mem.
brane Sci. 64, 1-11 (1991)). However, solvents comprising a saturated low molecular weight polymer of chlorotrifluoroethylene having a boiling point greater than about 280 ° C.
It is not suitable for the above-mentioned polymers.

Therefore, it is required that a solvent having a boiling point lower than or equal to the melting temperature of the polymer can be used. At such temperatures, the solvent becomes very volatile. If the use of an air gap results in a rapid loss of solvent into the air gap, the polymer concentration on the fiber surface can be increased, resulting in a low permeability surface coating. The mold outlet is submerged in a cooling bath to prevent skin formation caused by rapid evaporation of the solvent.

Although seemingly simple, submerged extrusion is actually extremely difficult to put to practical use. In the TIPS process, the heated extrudate passes through an air gap,
Contact cooling surface or cooling bath. The air gap is the distance from the mold outlet to the cooling surface or the solidification surface, and plays a very important role in extracting the melt. Pull-out is defined by the ratio of the wall thickness of the membrane to the groove space of the mold. With the air gap, the melt can be pulled out at an accelerated speed, and the melt can be drawn out at a high speed and at an economical speed. However, in hollow fiber immersion extrusion, when extruded from a mold into a cooling bath, the extruded fibers are rapidly cooled and solidified. Therefore, resistance at the time of pulling out increases. If it is not completely solidified, it tends to break. Therefore, with a low drawing rate,
It is necessary to spin the fibers.

In the present invention, immersion extrusion can be performed completely, and no air gap or the like is required. First, the hollow fiber mold is about 35
It is fabricated with a mold gap that is unusually narrow, 0-400 μm. This mold gap determines the wall thickness of the fiber membrane. The size of this gap is very close to the final fiber size and requires only a minimal pull-out operation. The mold is designed and processed so that only a chip having a size of about 1/16 inch is in contact with the coolant. Such changes are important in ensuring the method. Since the temperature of the cooling medium is sufficiently lower than the temperature of the mold body, the temperature of the mold is lowered by immersing the general-purpose mold, so that the solution cannot be sufficiently circulated. Even if only the mold tip is submerged, the temperature of the tip is reduced. In this case, a micro-thermocouple and a strategically arranged booster heater are used to control the temperature of the mold tip and increase the solution temperature at the mold tip.

The fibers can be extruded horizontally or vertically, as is evident from FIGS. 1 and 2. The solution is metered by volume through an annular mold by a metering pump to approximately match the working capacity of the spin line. This is to prevent drawdown of the fibers and breakage of the fragile extrusion. The inner and outer diameters of the mold and the groove spacing are set to the sizes necessary to obtain the final fiber. To obtain a practical fiber membrane, the wall thickness should be 100-250 μm, preferably 150-200 μm. The working efficiency of the spin line depends on the fiber size and the extrusion speed. Operations at processing speeds of about 20-200 feet / minute can be performed, with a preferred processing speed being 100 feet / minute.

During fiber extrusion, the inner diameter of the mold is filled with a continuous fluid to prevent the fiber lumen from collapsing. The flow rate of the rumen liquid needs to be carefully controlled to prevent uncontrollable changes in the fibers. The liquid is required to have a sufficiently high boiling point so that it does not boil in the mold or the extruded fibers. Such boiling causes air bubbles in the lumen and fiber breakage. By making the inner surface of the fiber membrane dense, the lumen liquid is prevented from affecting the inner wall surface of the fiber membrane. For example, at the contact interface between the rumen liquid and the inner wall surface, by solidifying the heated solution or by extracting the solvent from the interface, to increase the polymer concentration on the surface. The rumen liquid is metered into the mold at room temperature and preheated to 200 ° C.

The mold is comprised of a standard crosshead mold, which has a mold nose. This mold has two temperature control regions. The front of the mold is kept in a temperature range of 270-320C, preferably 280-290C. The mold nose includes a mold outlet and is at 290-320 ° C, preferably at 300 ° C.
Control to -310 ° C. The mold nose heating region can easily raise the solution temperature to a temperature near or above the boiling point of the solvent.

FIG. 1 shows a mold nose used for vertical fiber spinning. The solution is introduced from the crosshead mold into the circulation port 3 and transported to the mold outlet 3. The lumen liquid is introduced into the mold nose at the inlet 2 and is discharged from the mold outlet. The heater 5 is
The solution is kept in a molten state. The temperature sensor 6 maintains the heater 5 at a predetermined temperature of the solution separation temperature together with the temperature control device. The die 9 is submerged in the cooling bath 7. The gel-like hollow fiber membrane 8 is discharged from the mold nose through the mold outlet 9 together with the lumen liquid filling the inner diameter of the fiber membrane.

FIG. 2 shows a mold nose used for horizontal fiber spinning. The solution is introduced from the crosshead mold into the circulation port 13 and transported to the mold outlet 21. The lumen liquid is introduced into the mold nose at the inlet 12 and discharged from the mold outlet. The heater 15 holds the solution in a molten state. The temperature sensor 16 holds the heater 15 at a predetermined temperature of the solution separation temperature together with the temperature control device. Mold tip 2
2 is in contact with the cooling liquid 7 held in the cooling bath trough 20 through the mold nose and the insulating wall 19 of the cooling liquid. The gel-like hollow fiber membrane 18 is discharged from the mold nose through the mold outlet 9 together with the lumen liquid filling the inner diameter portion of the fiber membrane.

In the vertical extrusion, the die tip is arranged such that the gel fiber membrane to be extruded passes through an air gap and then contacts a cooling bath. Preferably, it is located about 1/16 inch (1.6 mm) in the submerged mold, as shown in FIG. In horizontal fiber spinning, the mold is firmly fixed to an insulating wall as shown in FIG. The die tip penetrates through an opening that provides liquid sealing properties to the insulator. The trough for the cooling liquid flow is located in the recess opposite the insulating seal so that the mold nose outlet remains submerged. The trough is fixed or retractable. Troughs have different depths. If the trough has a uniform depth, it is possible, for example, to remove the overflowed coolant by means of a pump. The cooling medium flows in the trough, overflows in a shallow region in the trough, and keeps the mold nose outlet flooded by the cooling medium.
The trough can be arranged, as appropriate, such that the coolant flows slightly between its end face and the insulating face.

[0054] PFA and PTFE / PFVAE copolymers exhibit chemically similar structures. However, PTFE / PFVAE copolymer is completely different from PFA in productivity. PFA tended to solidify in a very short time due to its high melting temperature. As a result, in submerged extrusion, if the lumen liquid is not controlled to a temperature within 260-280 ° C, 40-5
It was difficult to spin at a high speed of 0 fpm. High-speed spinning has been extremely difficult because rumen liquids tend to boil at the above temperatures. Under favorable conditions, the maximum spinning speed of PFA was 24.4 m / min (mpm) (80 ft / min). Perhaps due to its relatively low melting temperature, PT
The FE / PFVAE copolymer did not solidify in such a short time. Spinning speed is 5
It could be improved to 5.9 mpm (180 fpm).

The gel-like fiber membrane, ie, the dried and extracted fiber membrane, was able to elongate in the longitudinal direction and increase the transmittance.

Cooling bath The cooling bath lowers the temperature of the extruded fiber membrane below the upper critical solution temperature, causing phase separation. The cooling liquid is composed of a liquid having a sufficiently high boiling point so that bubbles are not generated when the fiber membrane is extruded from the mold and the step of forming surface holes is not adversely affected. The temperature of the cooling bath is 25-230 ° C, preferably 50-150 ° C.

The cooling liquid is required to consist of a liquid that does not boil at the cooling temperature or that does not boil when the heated extrudate is placed in the cooling bath. Further, it is necessary to form a skin by reacting with a fiber membrane or to form a liquid that does not boil when the polymer is decomposed or expanded at a cooling bath temperature. Preferably, dimethyl silicone oil and dioctyl phthalate can be exemplified. Further, a disubstituted phthalate can also be used.

The extruded and dried gel-like fiber membrane is introduced into a liquid phase extraction bath to remove the solvent without substantial softening, embrittlement, or decomposition of the fiber membrane. Examples of the extraction solvent that can be used include dichlorofluoroethane, HCFC-141b, 1,1,2-trichlorotrifluoroethylene (trade name “Freon TF” manufactured by DuPont), and hexane. The extraction is performed at about 20-50 ° C to minimize the effect of solvent extraction on the fiber membrane. The extracted fiber membrane is dried under conditions that do not shrink. For example, on a cylindrical core at 20-50 ° C. After that, the fiber membrane
Heated at 200-300 ° C.

The advantage of the immersion extrusion method is that the hollow fiber membrane can be continuously manufactured to a practical length. The fluorinated thermoplastic hollow fiber membrane produced by the conventional method was easily broken during the extrusion process, and a practical length could not be obtained. Membranes made by submersion extrusion show good permeability, exhibiting high surface porosity.
5 and 6 show the fiber membrane of Example 1 and the inner and outer surfaces of sample # 3. The inner surface has an epidermis-free surface made of nodules. The outer surface is composed of a structure oriented in a fibrous form.

FIGS. 7 and 8 show the inner surface and the outer surface of the fiber membrane of Example 1 and Sample # 8, respectively. The inner surface shows a fiber structure consisting of a spiral pattern, and the outer surface shows a mainly oriented fibrous structure. 9 and 10 show the inner surface and the outer surface of the fiber membrane of Sample 5. FIG. Both surfaces have high porosity,
There are no smooth areas. The above drawings show various high porosity or non-skinless surfaces, which were produced in a continuous process by the above-mentioned immersion extrusion method. The high surface porosity of the surfaceless coating in the present invention is hardly buried or stained by the fine particles during the filter operation. This indicates that the fiber membrane of the present invention can be used efficiently for a long time.

FIG. 3 is a diagram showing a typical vertical spinning step for producing the hollow fiber membrane of the present invention. The polymer / solvent paste mixture is introduced into the heated barrel extruder 31 through an inlet 32 by pump means, for example, a progressive cavity pump. The solution is formed in a heating barrel of the extruder 31. The extruder 31 conveys the heated solution through a conduit 33 into a melt pump 34,
The solution is metered through a conduit 35 into a crosshead mold 36. If necessary, the solution is conveyed from the extruder 31 through the conduit 33 into the melt pump 34, then through the conduit 48 into the solution filter 49, and further through the conduit 35.
Through to the crosshead mold 36.

The solution flows into the mold nose 1 through the crosshead mold 36. There, the solution is formed into a hollow fiber shape. Lumen liquid is introduced from the mold mandrel 38 to the inner diameter of the hollow fiber solution being discharged from the mold. The lumen liquid is supplied to the mold mandrel 38 by the lumen liquid supply means 46.

In the case of vertical fiber spinning, the solution holding the lumen liquid is extruded vertically from the mold nose 1 into the cooling liquid 7 in the cooling bath 41 in the absence of an air gap. In the cooling bath 41, the solution is cooled to cause microscopic phase separation between the polymer and the solvent, and the gel-like hollow fiber membrane 8 is formed. After passing through the cooling bath 41 by the guide roller 43, the gel-like hollow fiber membrane 8 is
It is taken out by the roll 44. Next, the gel-like hollow fiber membrane 8 is removed from the Godet roll 44 by the cross winder 45.

FIG. 4 is a typical process chart of a horizontal spinning process for producing the hollow fiber membrane of the present invention. The polymer / solvent paste mixture is introduced into the heated barrel extruder 31 by pumping means, for example, a progressive cavity pump. The solution is
It is formed in the heating barrel of the extruder 31. The extruder 31 conveys the heated solution through a conduit 33 into a melt pump 34 and meters the solution through a conduit 35 into a crosshead mold 36. If necessary, the solution is conveyed from the extruder 31 through the conduit 33 into the melt pump 34, then through the conduit 48 into the solution filter 49, and further through the conduit 35 to the crosshead mold 36. .

The solution flows through the crosshead mold 36 and into the mold nose 1. There, the solution is formed into a hollow fiber shape. Lumen liquid is introduced from the mold mandrel 38 to the inner diameter of the hollow fiber solution being discharged from the mold. The lumen liquid is supplied to the mold mandrel 38 by the lumen liquid supply means 46.

In the case of horizontal fiber spinning, the solution holding the lumen liquid is transferred from the mold nose 1 through the mold / cooling bath insulating wall 19 to the cooling liquid in the cooling bath 51 in the absence of an air gap. Extruded into 20. In the cooling bath 51, the solution is cooled to cause microscopic phase separation between the polymer and the solvent, thereby forming the gel-like hollow fiber membrane 18.

The gel-like hollow fiber membrane 18 passes through the cooling bath 51 by the guide roller 43 and is taken out by the Godet roll 44. Next, the gel-like hollow fiber membrane 18 is removed from the Godet roll 44 by the cross winder 45.

The solvent is extracted using a solvent that does not substantially weaken the hollow fiber membrane and has no adverse effect. The fiber membrane is dried under an atmosphere that minimizes shrinkage. If necessary, the fiber membrane can be stretched in the longitudinal direction, and can be heat-set.

The fluorinated thermoplastic hollow fiber membrane of the present invention obtained as described above has an inner surface and an outer surface which are porous, and at least one of the surfaces has no skin. The fibrous membrane is then characterized by a flow time of 3000 seconds or less (described below).

Contactor Fiber Membrane The contactor fiber membrane of the present invention employs the same hollow fiber membrane manufacturing process as for porous membranes. However, there are some differences in the operation range of the process parameters.

The solids content in the fiber spinning solution is 25-40%, preferably 28
-33%. The paste is metered into the heat mixing zone of a conventional double screw extruder and heated to 270-320C, preferably 285-310C. In the extrusion of the fiber membrane, the thickness of the membrane wall is 50-250 μm, preferably 100-150 μm, to provide a practical fiber membrane. The outer diameter is 800-1200 μm, and the inner diameter is 400-700 μm. The working efficiency of the spin line depends on the size of the fiber membrane and the extrusion speed. In practice, it is carried out at a working efficiency of about 20-200 ft / min, preferably at a working efficiency of 100-150 ft / min.

During extrusion of the fiber membrane, the liquid is continuously flowed through the inner diameter of the mold to prevent the rumen fibers from collapsing. The lumen liquid flow rate must be carefully controlled to prevent uncontrollable fluctuations in fiber membrane size. Further, the lumen liquid flow rate needs to have a sufficiently high boiling point so as not to boil in the mold or the extruded fiber membrane. When the rumen liquid boils, air bubbles are generated inside the ruminant liquid and the fiber membrane is broken. The lumen liquid does not affect the inner wall surface of the fiber by making the inner surface of the fiber membrane dense. For example, by coagulating the heated solution at the contact interface between the lumen liquid and the inner wall surface, or by extracting a solvent from the interface to increase the polymer concentration on the inner surface. The lumen liquid is at room temperature or about 250 ° C., preferably 21 ° C.
While preheated to a temperature of 5-235 ° C, it is weighed into a mold.

The mold comprises a standard crosshead mold, which has a mold nose. The mold has two temperature control parts. The crosshead portion of the mold is maintained at 270-320C, preferably 290-310C. The mold nose includes a mold outlet and is at 290-350 ° C, preferably at 32 ° C.
Controlled independently at 0-340 ° C. The mold nose heating zone can easily raise the solution temperature to a temperature near or above the boiling point of the solvent.

The cooling bath reduces the temperature of the extruded fiber membrane below the upper critical solution temperature, which causes phase separation. The cooling bath liquid is composed of a liquid having a sufficiently high boiling point to prevent bubbles from being generated in the mold during fiber membrane extrusion and not to adversely affect the surface pore forming step. The cooling bath temperature is 25-230 ° C, preferably 50-15 ° C.
0 ° C.

Characteristic evaluation method (flow rate speed) A fiber membrane is wound around a polypropylene tube having a diameter of 1/4 inch and a length of 1 inch to prepare a two-fiber fiber membrane. Then, using a hot melt gun, the hot melt adhesive through the open end of the tube fixes the fiber membrane. Usually, the adhesive does not penetrate between the fiber membranes. In order to secure the fixing operation, the hot melt resin is also applied to the other opening of the tube. The length of the fiber from the fixed end to the end of the winding is about 3.5 cm. After the hot melt resin has solidified, the tube is cut so that the fiber lumens are exposed. Fiber OD is measured with a microscope. The tube with the wound fiber membrane is fixed in a test holder. Isopropyl alcohol (IPA) is filled in the holder and sealed. Gas pressure is 13.5 psi. The time to accumulate the IPA transmission is recorded.

(Sample Calculation) IPA flow rate = V / (TπODNL) IPA flow time (FT) = seconds required to collect 500 ml of IPA, calculated from the time required to collect a predetermined volume of IPA Where: V = permeate volume T = time OD = outer diameter of fiber membrane N = number of fibers L = 1 total length of exposed fibers from 1

(Observation of Bubble Formation) The fixed fiber membrane on the winding is attached to a bubble point test holder.
This fiber membrane is immersed in a glass container filled with IPA. Air pressure gradually increases within the fiber membrane lumen. The pressure at which the first bubble is generated on the outer surface of the fiber membrane is recorded as a bubble generation point.

(Average Bubble Generation Point) The average bubble generation point was determined using the same method as in ASTM F316-80. Curves showing the relationship between air flow and pressure through the fiber membrane samples were generated for dry samples and samples wetted with IPA. The average bubble point is the pressure at which the wet air flow is half of the dry air flow.

(SEM Image) The hollow fiber membrane sample is immersed in isopropyl alcohol or a mixture of isopropyl alcohol and water (50:50). Next, the wet sample is immersed in the water in which the alcohol has been replaced. The sample wetted with water is held in a tweezer and immersed in a liquid nitrogen container. After removing the sample, it is folded by bending using a set of tweezers. A sample cut to a size of about 2 mm was placed on conductive carbon (Stru
cture Probe Inc. West Chester PA). Microstructure observation was performed using an ISI-DS130c scanning electron microscope (International Scientific
Instruments, Inc, Milpitas, CA). Digitized images were recorded in TIF format using a delayed scanning image capture machine.

Example 1 Hyfron 620 (Ausimont) as a PTFE / PFVAE copolymer and HaroVac 60 as a halogenated carbon oil were mixed to prepare an 18% by weight paste.
Then, the paste was added to a Baker-Perk L / D = 13 double screw extruder.
Extruded into ins MPC / V using Moyno pump. Thereafter, it was operated at 200 RPM under horizontal fiber extrusion mode. Extrusion and operating conditions are shown in Tables 1 and 2 below. Zen
The melt was weighed into a hollow fiber mold using an ith melt pump. The size of the annular portion of this mold was about 400 μm. Heated halogenated carbon oil 10
00N was used as the lumen liquid to maintain the hollow portion of the fiber membrane.
The melt pump and the lumen liquid pump have a fiber membrane wall thickness of 200μ.
m and lumen were adjusted to 500 μm. The cooling bath consisted of dioctyl phthalate. After centering the lumen needle, the mold was submerged in the cooling bath to a depth of about 1/16 inch and the fiber membrane was taken up by Godet rolls. The fiber membrane was Genesolv 2000 (Allid-Signal, Morristown, NJ)
And then annealed at 275 ° C. The resulting fiber membrane properties are given in Table 3.

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

[Table 3]

(Example 2: Effect of elongation) A fiber membrane was produced in the same manner as in Example 1. That is, the PTF in HalVac 60
From an 18% solid solution of the E / PEVAE copolymer, extraction was performed, 100% elongation was performed, and annealing was performed at 275 ° C. The following table shows the improvement in permeability by elongation.

Example 3 Mixing of Tetrafluoroethylene-Fluorinated Methyl Vinyl Ether Copolymer (A) and Tetrafluoroethylene-Fluorinated Propyl Vinyl Ether Copolymer (B) Example 1 using three types of mixtures of A) and (B)
It was prepared in the same manner as described above. The solids content in the paste was about 20%. The pickup was performed at a speed of 50 feet / minute. The cooling bath consisted of 85 ° C. dioctyl phthalate. The conditions for fabricating the fiber membrane are given in Tables 4 and 5. Fiber membrane property data is provided in Table 6.

[0086]

[Table 4]

[0087]

[Table 5]

[0088]

[Table 6]

Example 5: Tetrafluoroethylene-hexafluoroethylene copolymer (FEP)
The process conditions for spinning the FEP hollow fiber membrane were set the same as for each of the blended membranes of Example 4. However, the barrel temperature and the mold temperature were set differently. Also, a paste having a solid phase component of 20% was used. The dissolution temperature of FEP at about 258 ° C. is much lower than that of PFA or PTFE / PFVAE copolymer, even though it is much lower compared to tetrafluoroethylene-methylvinylvinylethylene copolymer . To spin the FEP, the barrel temperature needs to be raised to 295-305 ° C and the mold nose needs to be raised to 300-320 ° C. The membrane characteristics of the FEP hollow fiber membrane were such that the bubble generation point by IPA was 12.6 psi, the average bubble generation point was 40 psi, and the flow time was 1593 seconds.

(Comparative Example) A solution containing 19% of tetrafluoroethylene-propyl propylvinyl ether in halogenated carbonized oil 56 produced through the same process as that of Example 1 of USP 5,032,274 to form a hollow fiber membrane was used. Halocarbon 1000N 150 with low solubility in polymers
Extruded into a cooling bath at ℃. The extrusion barrel temperature was 1 for each of regions 1-4.
50 ° C, 285 ° C, 260 ° C, and 280 ° C were set. The melting temperature was 308 ° C. The extruder was operated at 300 rpm. The lumen liquid pump is 28-
The operation was performed at 30 rpm.

A portion of the hollow fiber membrane was made uncoated with the solvent by withdrawing at a rate of 55 feet / minute. The air gap between the mold outlet and the cooling bath is 0.2
5 inches. The OD of the obtained fiber membrane is 1500 μm and the wall thickness is 250
μm. The IPA flow time was 42,735 seconds.

A portion of the hollow fiber membrane was produced at a rate of 50 ft / min and coated with a solvent. Halocarbon 56 was extruded with the fiber membrane.
The air gap was 0.50 inches, the OD was 2000 μm, and the wall thickness was 250 μm. The IPA flow time was 3315 hours.

[0093] From these examples, the fiber membrane obtained by the initial method cannot achieve the desired characteristic of low flow time. Low flow time means that the membrane has high permeability and the time required for filtering is short.

Example 6 In this example, the skinless contactor hollow fiber membrane made from the 30% solution described above was replaced with our serial number (still unapproved) MCA
This was compared with the epidermal fiber membrane produced according to the method of 422. A gas mixture containing ozone and having high water solubility was brought into contact with water using these fiber membranes.

A skinless contactor fiber membrane was made in the following manner. Hyflon MFA (Ausimont, Tho
rofare, NJ) into HaloVac60 (Halocarbon Oil Inc Halocarbon Products Corp.)
oration, River Edge, NJ) to make a paste with a polymer content of 30%. This paste was then transferred to Ba using a Moyno melt pump (Springfield, OH).
The feed was to a ker-Perkins double screw extruder (Saginaw, MI). The extruder barrel temperature was set between 180-288 ° C. The melt was weighed into the hollow fiber mold using a Zenith melt pump (Waltham, MA). The size of the annular portion of the mold was about 300 μm. Halocarbon 60, a halogenated carbon oil, was fed into the lumen by a Zenith pump to hold the hollow portion of the fiber membrane. The melt pump and the lumen oil pump were adjusted such that the wall thickness of the fiber membrane was about 200 μm and the lumen was 700 μm. The temperature of the cooling bath composed of mineral oil was set at 70 ° C. After centering of the lumen needle, the mold was immersed horizontally in the cooling bath and the fiber membrane was pulled off at a rate of 100 feet / minute using a Godet roll. The fiber membrane was extracted with 1,1-dichloro-1-fluoroethane (Florocarbon 141b, Genesolve 2000 Allied-Signal, NJ) and then dried. This fiber membrane had an IPA bubble generation point of 40-50 psi or more, and an IPA flow time of 12,000 seconds. The penetration pressure of these fiber membranes was 8-10 psi.

Each contactor was set on a test table shown in FIG. And pH 6.2, temperature 23 ° C
Was supplied into the lumen of the fiber membrane at various flow rates. Water from a deionized water system (not shown) is sent into the valve 142 with the bypass valve 141 closed. Pressure gauges 150 and 151 measure the decrease in water flow pressure through the contactor. The ozone contactor 160 includes a surface coating (102698 units) or a non-surface coating (12798 units). Ozone gas from the Sorbious Semozon 090.2HP ozone generator has an inlet 13 at a flow rate of 2 standard L / min (slpm).
0 was supplied into the outer container of the contactor unit 160. The contactor gas pressure is measured by a pressure gauge 152 and controlled by a pressure controller 180. The outlet gas sensor 112 measured the ozone concentration on the outlet side. The decomposed ozone in the outlet flow of the contactor is measured by the ozone sensor 111. Decomposed ozone in the overflow rinse bath was measured by an Orbisphere Model 3600 decomposed ozone sensor 110. Liquid flow was varied between 3.6-20 lpm by adjusting valve 140 and inlet liquid pressure. The gas pressure on the outer vessel side of the contactor is sufficiently reduced to prevent the formation of bubbles in the liquid when the gas is transported through the fiber membrane into the liquid.

FIG. 11 is a plot of the amount of dissolved ozone (ppm) in the outlet stream versus the flow rate (L / min) of deionized water for each contactor. These results indicate that the amount of ozone in the outlet stream decreases as the flow rate of deionized water increases, and that the non-skinned fiber membrane contactor is more abundant in the deionized water than the skinned contactor (102698). Ozone can be dissolved.

(Example 7) The epidermal fiber membrane and the non-epidermal fiber membrane in Example 6 were compared and studied with respect to carbon dioxide which is a highly water-soluble gas. Each contactor used in this example was prepared by preparing a bundle of fiber membranes and then fixing and installing the bundle in a cylindrical holder. In each contactor, the lumen side was separated from the outer container of the fiber membrane, that is, the outer shell side. The fiber membrane ID was 500 μm, and the wall thickness of the fiber membrane was about 150 μm. 500 fibers
And its length was 43 cm. The contactor was tested for gasification efficiency. In this embodiment, water degassed at 20 ° C. by a Hoechst Liquid Cel degasser was pumped into the fiber membrane lumen. Also, air-containing carbon dioxide was sent through the outside of the fiber membrane with a low pressure drop. For practical purposes, the absolute value of the gas pressure was assumed to be 760 mmHg. The ozone gas concentration at the time of supply and in the outlet water flow was measured by changing the flow rate.

FIG. 13 shows the measurement result and a theoretical value based on the Leveque equation. The data analysis method is shown below. The mass transport coefficient K was calculated from the following equation. K =-(Q / A) ln [Cout-C ^* / Cin-C ^* ] where Cout is the carbon dioxide concentration (ppm) in the effluent liquid, and Cin is the carbon dioxide concentration ( ppm) and C ^* is the equilibrium carbon dioxide concentration (ppm) at the ambient gas pressure. Q is the flow rate (cc / s), and A is the membrane area (cm ² ).

The Sherwood number is calculated as follows. Sh = KD / Dab where K is the mass transport coefficient (cm / s), D is the fiber membrane ID (cm), and Dab is the diffusion coefficient of carbon dioxide in water (cm ² / s).

The Graetz number or Peclet number is calculated as follows. Pe or Gr = VD ² / (LDab) Here, V is the flow velocity (cm / s) inside the lumen, and L is the fiber length (cm).

The Sherwood number and the Graetz number are dimensionless quantities used to describe heat and mass transport operations. The Sherwood number is a dimensionless mass transport coefficient, and the Graetz number is a dimensionless quantity that is inversely proportional to interfacial layer thickness.

SRWickramasinghe et al., In “J. Menbrane Sci. 69” (1992), pp235-250, analyzed oxygen transport in hollow fiber membranes using the method of Leveque. At this time, one bundle of hollow fiber membranes was used. They showed that the plot of Sherwood number versus Graetz number is linear as the theoretical expectation where the Graetz number is large. Where the Graetz number is small, it is explained by the non-uniformity of the fiber membrane diameter and affects the non-uniformity of the flow through the fiber membrane. Their analysis is
At low Graetz numbers, the average mass transport coefficient drops below the theoretical value due to uneven flow through the fiber membrane. They conclude that oxygen mass transport is not affected by diffusion resistance through the fiber membrane. Conversely, it can be concluded that fiber membranes according to Leveque's theory are porous because the diffusion resistance is so high that they cannot flow according to said theory.

The results shown in FIG. 13 indicate that the surface-less coating of this example has a low film resistance to ozone because it obeys the above-mentioned Leveque's equation even when the number of Peclets is high. . In the linear region, when the Graetz number is between 5 and 1000, this Graetz number and
The correlation with the Sherwood number is given by Sh = 1.64 (Gr) ^0.33 .

[Brief description of the drawings]

FIG. 1 is a process chart of the production method of the present invention using vertical extrusion.

FIG. 2 is a process chart of the production method of the present invention using horizontal extrusion.

FIG. 3 is a view showing a mold used in vertical fiber spinning.

FIG. 4 is a view showing a mold used in horizontal fiber spinning.

FIG. 5 is a micrograph of a microporous hollow fiber membrane produced from a polytetrafluoroethylene-fluoroalkylvinylether copolymer produced according to Example 1 and an inner surface of Sample 3, which is magnified 3191 times.

FIG. 6 is a photomicrograph of an outer surface of a hollow fiber microporous membrane produced from a polytetrafluoroethylene-fluorinated alkylvinyl ether copolymer, prepared according to Example 1, which was enlarged 3191 times, on the outer surface of Sample 3.

FIG. 7 is a microphotograph at 3395 times the inner surface of a microporous hollow fiber membrane produced from a polytetrafluoroethylene-fluoroalkylvinylether copolymer produced according to Example 1, and the inside surface of which is sample 3 magnified 3395 times.

FIG. 8 is a photomicrograph of a microporous hollow fiber membrane produced from a polytetrafluoroethylene-fluoroalkylvinylether copolymer produced according to Example 1 and an outer surface of Sample 3, which was magnified 3372 times, in Sample 3;

FIG. 9 is a micrograph of the inner surface of a hollow fiber microporous membrane manufactured from polytetrafluoroethylene-hexafluoropropylene (FEP) manufactured according to Example 5 at a magnification of 984 times.

FIG. 10 is a photomicrograph at 1611 magnification of the outer surface of a hollow fiber microporous membrane produced from polytetrafluoroethylene-hexafluoropropylene (FEP) produced according to Example 5.

FIG. 11 is a graph comparing the performance of a hollow fiber membrane contactor manufactured from a membrane with a skin with a performance of a contactor made from a membrane without a skin by water ozonation treatment.

FIG. 12 is a diagram schematically showing a test method used for comparing a contactor in a state where a liquid phase is in contact with a liquid phase.

FIG. 13 is a diagram for comparing the adsorptivity of carbon dioxide in water of the contactors manufactured from the surface film and the surfaceless film, respectively.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW (72 Inventor Rungicant Be Patel, Massachusetts, USA 01876 Tewkesbury, Breckenridge Road 22 (72) Inventor Dean Tea Gates, Massachusetts, USA 01730 Bedford Nelian Way 27 F-term (reference) 4D006 MA01 MA25 MB20 MC28 NA04 NA10 NA16 NA40 NA64 4L035 BB03 DD03 EE20 FF01

Claims (29)

[Claims] 1. A hollow fiber porous membrane comprising a fluorinated thermoplastic polymer, wherein at least one surface is substantially skinless and has an IPA flow rate of less than about 3000 seconds. 2. The fiber porous membrane according to claim 1, wherein the porous membrane is asymmetric.
Issuance of hollow fiber porous membrane. 3. The hollow fiber porous membrane according to claim 1, wherein the IPA flow rate is less than about 2000. 4. The hollow fiber porous membrane according to claim 1, wherein the IPA flow rate is less than about 1500. 5. The fluorinated thermoplastic polymer is a tetrafluoroethylene-fluoroalkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. 2. The hollow fiber porous membrane according to item 1. 6. The method according to claim 5, wherein the alkyl group in the tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer is a propyl group, a methyl group, or a mixed group of a methyl group and a propyl group. 2. The hollow fiber porous membrane according to item 1. 7. A method for producing a hollow fiber porous membrane that is substantially skinless on at least one surface from a fluorinated thermoplastic polymer, wherein (a) the fluorinated thermoplastic polymer is Dissolving in a solvent that forms a supercritical solution temperature with the polymer; and (b) partially immersing the resulting solution in a cooling bath to prevent the solution from being pre-cooled. (C) extruding the solution into the cooling bath; and (d) cooling the solution to a temperature equal to or lower than the upper critical solution temperature. And performing a liquid-liquid phase separation into two phases of a polymer-rich solid phase and a solvent-rich liquid phase to produce a gel-like fiber; and (e) removing the solvent from the gel-like fiber. Extracting to form a porous hollow fiber membrane; and (f) the porous hollow fiber A method for producing a porous hollow fiber membrane, comprising the steps of: drying the membrane under controlled conditions. 8. The method for producing a porous hollow fiber membrane according to claim 7, wherein the immersed portion of the mold is a mold tip. 9. The method of claim 7, wherein the fluorinated thermoplastic polymer is dissolved in a solvent that forms a supercritical solution temperature with the polymer at a concentration of about 12-35% by weight. The method for producing the hollow fiber porous membrane according to the above. 10. The step (b) is extruded through an annular mold maintained at a sufficiently high temperature in an essentially horizontal state to prevent the solution from being pre-cooled. 8. The method of claim 7, further comprising the step of: separating the die from the cooling bath and penetrating a wall exposed at a die outlet to the cooling bath.
3. The method for producing a hollow fiber porous membrane according to item 1. 11. The method for producing a hollow fiber porous membrane according to claim 7, wherein the solvent has a boiling point lower than the gel-like fiber temperature at the die tip outlet. 12. The method for producing a hollow fiber porous membrane according to claim 7, wherein the solvent has a molecular weight smaller than that of saturated chlorotrifluorohydrocarbon. 13. The solvent may be HaloVac 60 or HaloVac 56.
The method for producing a hollow fiber porous membrane according to claim 12, wherein the method is a mixture of these. 14. The fluorinated thermoplastic polymer is a tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. The method for producing a hollow fiber porous membrane according to any one of the above. 15. The method according to claim 14, wherein the alkyl group in the tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer is a propyl group, a methyl group, or a mixed group of a methyl group and a propyl group. 3. The method for producing a hollow fiber porous membrane according to item 1. 16. The hollow fiber porous material according to claim 7, wherein the cooling bath liquid is composed of a solvent component that is insoluble in the fluorinated thermoplastic polymer. Method of forming a porous membrane. 17. The method for producing a porous hollow fiber membrane according to claim 14, comprising a solvent component insoluble in the fluorinated thermoplastic polymer. 18. The method for producing a hollow fiber porous membrane according to claim 7, wherein the cooling bath liquid is composed of silicone oil or dioctyl phthalate. 19. The method for producing a porous hollow fiber membrane according to claim 14, wherein the cooling bath liquid is composed of silicone oil or dioctyl phthalate. 20. A porous hollow fiber made of a fluorinated thermoplastic polymer, wherein at least one surface is non-skinned and has an IPA flow rate of less than about 3000, prepared by the method of claim 7-13. Membrane. 21. The hollow fiber membrane according to claim 2, wherein the hollow fiber membrane is asymmetric.
0. The hollow fiber porous membrane according to 0. 22. The method according to claim 20, wherein the fluorinated thermoplastic polymer is a tetrafluoroethylene-fluorinated alkylvinyl ether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. Hollow fiber porous membrane. 23. The alkyl group in the tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer, wherein the alkyl group is a propyl group, a methyl group, or a mixed group of a methyl group and a propyl group. 2. The hollow fiber porous membrane according to item 1. 24. The method according to claim 21, wherein the fluorinated thermoplastic polymer is a tetrafluoroethylene-fluoroalkylvinylether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. Hollow fiber porous membrane. 25. The method according to claim 24, wherein the alkyl group in the tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer is a propyl group, a methyl group, or a mixed group of a methyl group and a propyl group. 2. The hollow fiber porous membrane according to item 1. 26. A hollow fiber contactor membrane comprising a fluorinated thermoplastic polymer having a porous surface on both diameters. 27. Graetz having an epidermal surface on both diameters
In the range of 5-1000, this Graetz number is 0.33 to 1
. Hollow fiber contactor membrane made of fluorinated thermoplastic polymer, allowing liquid-gas phase mass transport with a Sherwood number equal to 64 times. 28. The fluorinated thermoplastic polymer is a tetrafluoroethylene-fluoroalkylvinylether copolymer or a tetrafluoroethylene-hexafluoropropylene copolymer. 2. The hollow fiber contactor membrane according to item 1. 29. The method according to claim 28, wherein the alkyl group in the tetrafluoroethylene-fluorinated alkyl vinyl ether copolymer is a propyl group, a methyl group, or a mixed group of a methyl group and a propyl group. 2. The hollow fiber contactor membrane according to item 1.